1. Field of the Invention
This invention relates to an all-terrain vehicle (ATV), and more particularly to an ATV having an improved suspension system.
2. Description of Related Art
ATVs are generally operated in fairly rough terrain or, at least, must be capable of operating in rough terrain. Therefore, in addition to the obvious requirement of providing a smooth ride, suspension systems for ATVs must be strong and allow for a relatively large amount of wheel travel.
Wheel travel is provided in an ATV, among other things, by utilizing relatively long suspension arms. Long suspension arms allow the wheels to move relative to the frame within a large arc with the pivot point provided by suspension arm mounts on the frame. Shorter suspension arms do not provide adequate wheel travel for ATV applications. Furthermore, the necessary handling characteristics of an ATV also necessitate relatively long suspension arms. In particular, during wheel travel, wheels connected to the suspension arms move horizontally, as well as vertically, due to the pivotal nature of the movement. Specifically, for a swing arm or trailing arm configuration, the wheels move horizontally in forward and rearward directions (longitudinally relative to the ATV) during wheel travel and for an A-arm configuration, the wheels move horizontally in inward and outward directions (transversely relative to the vehicle). Shorter suspension arms maximize this horizontal movement such that the wheel base length of the vehicle or lateral spacing of the wheels (depending of the type of suspension configuration) varies greatly over the range wheel travel. In contrast, longer suspension arms reduce this horizontal wheel travel, such that the wheel base length of the vehicle of the lateral spacing of the wheels remain substantially constant through the range of wheel travel.
Additionally, a great deal of ground clearance is preferable to allow traversal of rough terrain. The long suspension arms of an ATV allow the sprung portion of the ATV (those components of the ATV that are attached to the frame) to be disposed relatively high above the ground. Typically, the suspension arms depend somewhat from the suspension arm mounts on the frame to increase the ground clearance. Furthermore, sprung components are usually disposed above a lower most portion of the frame to prevent hang-ups of these components while traversing rough terrain.
There are several types of ATV suspension systems, which have been designed to meet the specialized criterion. One type, shown in FIG. 1, is a fully dependent type suspension system indicated at 700. This suspension system includes a single rigid swing arm 702 pivotally mounted to a frame 704 on one end thereof and rigidly mounted to a single rigid axle 706 on an opposite end thereof. As shown in FIG. 1, a left side wheel 708 is connected to a left end of the axle 706 and a right side wheel (not shown) is connected to a right end of the axle 706.
This type of suspension system is simple in design and relatively inexpensive to manufacture. However, since the axle 706 and swing arm 702 are rigid, both wheels move in response to terrain acting on either wheel. As such, this type of suspension system provides a relatively rough ride.
Alternatively, to improve rider comfort, other known types of suspension systems have been designed with independence of movement between forward or rearward pairs of suspension arms. This type of system allows each wheel of the respective pair to move independently from the other wheel, thereby providing a smoother ride. One such type of suspension system is a double A-arm or double-wishbone suspension system. However, this type of suspension system is complex and highly costly to manufacture.
One other type of suspension system is a semi-independent type, such as shown at 800 in FIGS. 2 and 3. As shown, this system includes left and right pairs of A-arms 802, 804. Additionally, the system 800 includes a stabilizer bar 810, which is shown connecting at ends thereof to an upper A-arm of each pair of A-arms 802, 804 and extends therebetween. The stabilizer bar 810 is torsionally deflected by relative movement between the pairs of A-arms 802, 804. The torsional deflection of the stabilizer bar 810 allows the pairs of A-arms 802, 804 a degree of virtually independent movement. However, the stabilizer bar 810 develops a degree of torsional stiffness once deflected to a certain point and, at such time, further movement of one of the pairs of A-arms 802, 804 imparts a corresponding movement of the other pair of A-arms 802, 804. In this manner, the A-arm pairs 802, 804 are allowed virtually independent movement over a range and beyond this range move dependently. This type of system prevents excessive roll movement of the ATV during maneuvering, which is problematic with fully independent suspension systems. However, as with the fully independent system, the semi-independent suspension system, as shown in FIGS. 2 and 3, are complex and costly to manufacture.
Furthermore, to date, there has not been a suspension system developed for an ATV that is adjustable in the degree of dependence provided between respective suspension arms. This feature would be advantageous since desired handling characteristics for one terrain situation or one particular rider may not be suitable or comfortable for another terrain condition or rider.